In recent years, there has been an ever-increasing demand for power electronics to drive LED based lighting systems. Along with this is the demand for improving the power quality of the AC systems supplying the power electronics. Various options are available to improve the power quality of AC systems. One of the options that is gaining in popularity is the active shaping of the input line current (i.e., active Power Factor Correction (PFC)), since it makes the load appear as a pure resistance, leading to near unity load power factor and generating negligible harmonics in the input current.
One well-known active PFC LED driver is a two-stage Boost-Buck power supply circuit. With this type of circuit, a boost stage acts as a front end PFC due to its smoothly varying input current and simplicity, and buck stage acts as the LED driver. In spite of its simplicity, this two-stage active PFC LED driver requires two different control circuits to harmonize the input current and to regulate the current through the LEDs. In addition, the boost stage can exhibit start-up over-currents, which can require additional protection circuitry.
Another well-known active PFC LED driver is a single-stage SEPIC ( ) PFC driver. This type of driver uses only one switch to harmonize the input current and to regulate the current through LEDs. Although the single-stage SEPIC uses only one switch, and thus one control circuit, it too exhibits certain drawbacks. Namely, this driver type includes a bulk storage capacitor and an output diode, which requires more board space and increases the weight of the driver.
For space constrained LED applications, such as aerospace exterior lighting applications, one of the key objectives is to provide an optimized solution from weight, volume, and cost perspectives. Moreover, for retrofit applications, providing a solution that is an integrated power supply provides the advantage of a drop-in replacement for existing filament based light systems with LED based light systems.
Hence, there is a need for a power factor corrected LED driver circuit that does not rely on multiple switches, a bulk storage capacitor, and an output diode, and/or provides optimized solution from weight, volume, and cost perspectives. The present invention addresses at least these needs.